The goal of this project is to define the molecular mechanisms governing neural tube closure. Neural tube defects (NTDs) are amongst the most common human structural congenital malformations. In this project, we focus on a highly expressed microRNA family in pluripotency, miR-302, which plays a critical role during neural tube closure. Using genetic loss-of-function mouse, chicken and human models, we find that miR-302 is required to prevent precocious differentiation of the neuroepithelium. Additionally, we present data suggesting that miR- 302 is mutated in humans with neural tube closure defects. This project will provide insight into the earliest stages of neural tube development and inform our understanding of how microRNAs control this critical process.